DE19840527A1 - Production of indium-tin oxide suspensions and powders for production of coatings for microelectronic and optical products comprises precipitation and processing in presence of surface modifying agent - Google Patents

Abstract

Process for the production of indium-tin oxide suspensions, powders and molded articles comprises precipitation of precursors in the presence of a surface modifying agent, calcining the resulting powder and comminuting the powder with a surface modifying component. Suspensions, powders and molded articles of indium-tin oxide (I) are prepared by (A) precipitation of indium oxide and tin oxide precursors from solution in the presence of at least one surface modifying component; (B) calcining of the resulting powder after removal of the solvent; (C) addition of a surface modifying component and a solvent; (D) subjecting the resulting mixture to a comminution or dispersion treatment; (E) optionally removing liquid components to yield a powder; and (F) optionally forming the powder into a molded article.

Description

The invention relates to a method for producing suspensions, powders and Shaped bodies of indium tin oxide, the products obtainable thereby and their Use.

Indium tin oxides are known for their optoelectronic properties draws. You are e.g. B. in the form of thin transparent layers capable To reflect infrared light and at the same time are characterized by a relatively high electronic conductivity with existing transparency in layer systems. For this reason there are many possible uses for Indi um tin oxide (ITO) systems, and accordingly a lot of research their manufacture.

The most common methods for applying transparent layers are gas phase techniques in which the ITO from the gas phase onto the substrate in the form of a coherent thin layer is deposited. As a different process the sol-gel process or powder and paste technologies are used.

The indium and oxygen system is characterized by a large number of compounds. The most thermodynamically stable is In ₂ O ₃ . Indium oxides of the composition In ₄ O ₃ , In ₄ O ₅ , In ₂ O and In ₇ O ₉ are usually formed by reducing In ₂ O ₃ in a hydrogen stream. In ₂ O ₃ is dark yellow to light yellow at room temperature, brown to brownish red at higher temperatures and soluble in mineral acids. Only the cubic modification can be detected by X-ray.

In the literature, the production of pure indium oxide powder is predominantly used Precipitation from solutions described. The chosen hydroxides are then converted into the oxides by calcining. Aqueous salt solutions are included Alkali solutions, precipitated with ammonia or with urea; see e.g. B. JP 06227815 A2, JP 05193939 A2, JP 04325415 A2, JP 04219315 A2 and DE 21 27 135 A.  

Sometimes the precipitation takes place in the presence of sulfuric acid or sulfate solutions; see e.g. B. JP 05058627 A2. However, there is no information about the influence of the precipitant on the powder quality. Also contains the literature no or very inaccurate information on particle size or agglomeration state. The particle sizes that are usually obtained from the measurements of the BET surface area Powder calculated back extend from the nanometer range to the 100 µm range.

Indium oxide is a wide-gap semiconductor, the intrinsic electron conduction of which Oxygen vacancies is based. In addition to intra crystalline effects mainly through the hindrance of intercrystalline electrons limited transitions. One possibility, the low charge density of the Increasing pure indium oxide is the targeted incorporation of tetravalent elements such as B. tin.

Various ways of producing indium oxide-tin oxide mixtures are known. In the simple mixed oxide process for the production of ITO mixtures, temperatures between 700 ° C and 900 ° C are required; see e.g. B. EP 654 447 A1. The sol-gel technique is also suitable for the production of ITO mixtures, with specific powder surfaces of 10 m ² / g being specified; see e.g. B. JP 06293517 A, JP 06080422 A and JP 05201731 A. Furthermore, electrolysis processes are described in which hydroxides are produced by anodic oxidation of an indium electrode or an indium tin electrode, which are converted into oxides by subsequent calcining; see JP 63195101 A2, JP 06171937 A2 and JP 06329415 A2. Indium tin hydroxides are also dispersed in organic solvents, dehydrated by azeotropic distillation and then converted into the oxides by drying and calcination; see JP 02006332 A2. ITO powders can also be armed by an arc discharge between a tungsten electrode and an indium electrode in an argon-oxygen mixture (Y. Endo et al., Funtai, Kogaku Kaishi (1995), 32 (12), 874-80) Aerosol spray pyrolysis of indium acetate in water in an argon carrier gas (DM Speckmann et al., Mater. Res. Soc. Symp. Roc. (1995), 372 (Hollow and Solid Sphere and Microspheres: Science and Technology Associated with Their Fabrication and Application), 247 -52 or by spraying indium tin salt solutions at 800 ° C. (JP 01087519 A) Indium oxide or tin oxide can also be produced by condensation of indium chloride and tin chloride from the gas phase and subsequent reactions with oxygen or water (JP 05024836 A2) a corona discharge in a reducing atmosphere at 1000 ° C (DE 44 07 774 C1).

For the production of ITO layers, for. B. directly used ITO powder. So use z. B. JP 07118840 A is an ITO powder with a specific surface area of 30 m ² / g, JP 06049394 A is an ITO powder with a diameter of 200 nm and JP 05036314 A is an ITO powder with an average particle size of 30 nm.

In summary, this means that there are a large number of manufacturing processes for tin-doped indium oxide (ITO) powder. However, defined information about powder qualities in connection with their method of manufacture are not described. The quality of the powder used is usually defined by the application. In recent years, the interest in a defined production and application of transparent conductive layers on various substrates has become increasingly important. While the use of Sb- and F-doped tin oxide has long been known on glass substrates due to its conductivity, its transparency in the visible spectral range and its reflection properties in the IR range for the surface heating of glasses for aircraft, spaceships, cameras and also for electrostatic shielding purposes, In recent times, diverse requirements have been placed on such layers for applications in microelectronics and optoelectronics. These include e.g. B.

• 1. transparent control electrodes for liquid displays, thin film electro luminescent displays and electrochromic displays
• 2. transparent conductive layers for highly sensitive radiation detectors, ferroelectric photoconductors and memory devices  
• 3. transparent conductive oxide films as gate electrodes for charge, Injection and charge coupled devices.

These applications in optoelectronics are also higher Conductivity, transparency and structurability requirements Layers connected. Because of the unfavorable structuring properties doped tin oxide layers in the usual structuring by chemical Etching technologies have predominantly tin doped for these applications Indium oxide layers (ITO) prevailed.

Furthermore, these ITO layers show a significantly better conductivity and transparency compared to doped tin oxide layers. Tin-doped indium oxide layers are currently the most conductive coatings that are commercially available. In routine operation, the achievable specific resistance is about 1 - 2 × 10 ^-4 Ohm.cm, which in connection with an approximately 30 nm thick barrier layer made of SiO ₂ already leads to a surface resistance of 15 Ω / with a layer thickness of 120 nm. (Transparency <90%). Due to the production in the sputtering or CVD process, the costs for this type of coating are comparatively high and large-area coatings are difficult to carry out.

The high charge carrier density in connection with charge carrier mobility in the range of 40-60 cm ² / Vs leads to a very high transparency in the visible range, with at the same time excellent reflection in the IR range. The proportion of tin oxide is usually between 7-12% by weight.

For many areas of application, especially in micro and optoelectronics Optical and IR reflective coatings, it is important that ITO powder are used, which consist of nanoscale particles. Such nanoscale Particles have an average particle size of preferably not more than 200 nm, in particular not more than 50 nm and particularly preferably not more than 30 nm on. A particularly preferred range is 5 to 30 nm.  

In many processes for the production of indium tin oxide powders or suspensions ions, suspensions of precursors of the indium tin oxide powder are obtained, from which after drying the indium tin oxide powder by calcination getting produced. However, the particle sizes of the powders produced in this way are not in the desired nm range and the powders can also not again Suspensions with particle sizes in the nm range (nanoscale particles) worked up are, so that with such low viscosity suspensions Coatings by dipping, spraying or similar processes with particle sizes in nm range can be produced.

The ITO powder precursors are formed in suspension among the suitable conditions nanoscale primary particles of suitable size, in which Working up, especially in the calcination, aggregate these primary particles but to larger particles. This aggregate formation is due to the fact that with decreasing particle size also weak interaction forces, such as B. van der Waals forces, gaining significant importance or dominating. On top of that the particle surface always with functional, d. H. condensable, groups is evidenced by condensation reactions between individual primary particles Form hard aggregates. The primary particles are then virtually over sintered necks connected with each other. These aggregates consisting of primary particles can by a simple dispersion step in a non-aqueous or aqueous Solvent can no longer be broken open.

Such powders produced by calcination cannot be used for highly trans Parent layers are used, since particles with sizes over 50 nm are already too cause optical interference.

The object of the present invention was therefore to make suspensions, powders and To produce moldings based on tin indium oxide so that despite Calcination of nanoscale particles with a suitable size can be obtained and the Powder processed into suspensions in a simple dispersion step can be, whereby the primary particle size is completely retained.  

This is achieved according to the invention by a process for the production of suspensions, powders and moldings of indium tin oxide, which is characterized in that

• a) Indium oxide and tin oxide precursors in the presence of one or more upper surface-modifying components from solutions in one or more Solvents are precipitated,
• b) the powder obtained is calcined after removal of the solvent,
• c) one or more surface-modifying components and one or several solvents are added
• d) the mixture obtained is a grinding or dispersing treatment will throw
• e) liquid components are optionally separated from the suspension, to get a powder
• f) optionally the powder obtained in a molding process Shaped body is transferred.

Surprisingly, suspensions, Obtained powder and moldings based on indium tin oxide, which in essentially consist of primary particles and essentially none Contain aggregation of primary particles formed agglomerates. Leave the powder easily redisperse into suspensions in which the primary particle size remains practically completely intact.

Taking an indium tin oxide powder, which is also referred to as ITO powder understood a powder consisting essentially of a mixed oxide of indium and Tin exists. The indium and the tin can be in one or in different Oxidation levels are present. For example, there are In (+ I) and / or In (+ III) as well Sn (+ II) and / or Sn (+ IV). Sn is preferably present as Sn (+ IV). Possibly indium and tin can also be partially present as In (0) or Sn (0). On the The surface of the particles of ITO powder are also those described below surface-modifying components available.  

The ITO powder is preferably a tin-doped indium oxide, ie the proportion of tin oxide is less than the proportion of indium oxide. The proportion of tin oxide based on the indium-tin oxide, without taking into account the surface-modifying component, is, for example, 2 to 30 mol%, preferably 7 to 12 mol%. The ITO powder can be expressed, for example, without taking into account the surface _- modifying component, by the formula In _2-y Sn _y O ₃ with 0 ≦ y <2, in particular 0 ≦ y <1 (excess charge: e⁻ _y ).

Of course, the indium tin oxide powder can contain impurities. The acceptable level depends on the purpose. About the educts z. B. SO ₄ ^2- , Ca, Co, Cu, Fe, Ni, Pb, Zn, K or Na may be included. By using pure starting materials, SO ₄ ^2- , Ca, Co, Cu, Fe, Ni, Pb and Zn can be brought to below 0.005% by weight and Na, K to below 0.01% by weight. About the method, for. B. NH ₄ ⁺ and Cl⁻ get into the product, which can be virtually completely removed depending on the number of washing cycles. Based on the indium tin oxide powder, but taking into account the surface-modifying component, less than 5% by weight, preferably less than 1% by weight, particularly preferably less than 0.1% by weight, of impurities are present.

In the process according to the invention, indium oxide and tin oxide precursors are formed in Presence of one or more surface-modifying components one or more solvents.

The precipitation process or the co-precipitation process can be any of these act according to methods known in the art. The precipitation can for example via a sol-gel process, an electrolysis process Dehydration process or an aerosol spray pyrolysis process as they are described above. Precipitation is preferred but through a sol-gel process. In the sol-gel process, at Presence of water e.g. B. by adding bases or acids hydrolysis and Condensation reactions initiated to precipitate hydroxo (oxo) con  lead data. In doing so, the indium oxides and tin oxide are precipitated Precursors particularly preferably bases, especially primary, secondary, tertiary aliphatic or aromatic amines, tetramethylammonium hydroxide, NaOH, KOH, Ammonia, ammonium hydroxide or mixtures thereof are used. Especially ammonium hydroxide is preferably used for the precipitation.

As indium oxides and tin oxide precursors, all indium and tin Compounds are used, from which by precipitation and optionally subsequent post-processing, such as calcination, indi um tin oxide powder can be obtained. Naturally, the choice of Indium and tin compounds after the precipitation process used For example, indium electrodes or indium tin can be used in electrolysis processes electrodes and in dehydrogenation processes indium tin hydroxides as indium oxides and tin oxide precursors.

Preferred indium oxides and tin oxide precursors are, especially in the case of sol-gel precipitation indium chloride, indium iodide, indium nitrate, indium acetate, Indium sulfate, indium alkoxides, such as indium methoxide or indium ethoxide, or Mixtures thereof or tin chloride, tin sulfate, tin alkoxides, such as tin methoxide or tin thoxide, or mixtures thereof, with tin in the oxidation state +2 or +4 and indium in the oxidation state +3 or with chloride and iodide also in oxidation level +1 is present.

The indium oxide and tin oxide precursors are combined from one or like several solvents. The indium oxide and tin oxide precursors are preferably completely dissolved in the solvent (s). As a solvent water and / or organic solvents are preferably used. On distilled (pure) water is a particularly preferred solvent. As organic Solvents are suitable for both polar and non-polar and aprotic ones Solvents Examples of these are alcohols, such as. B. aliphatic alcohols with 1 to 6 Carbon atoms (especially methanol, ethanol, n- and i-propanol and butanol); Ketones such as B. acetone and butanone; Esters such as B. ethyl acetate; Ether like  e.g. B. diethyl ether, tetrahydrofuran and tetrahydropyran; Amides such as B. Dimethylacetamide and dimethylformamide; Sulfoxides and sulfones, such as. B. Sulfolan and Dimethyl sulfoxide; and aliphatic (optionally halogenated) hydrocarbons, such as B. pentane, hexane and cyclohexane. Mixtures can of course also be used such solvents are used.

The solvent used preferably has a boiling point which is one easy removal by distillation (possibly under vacuum) enables. Solvents with a boiling point below 200 ° C. are preferred especially below 150 ° C.

The precipitation takes place in the presence of surface-modifying components. The surface-modifying component (s) can be for example short-chain organic molecules. Such connections preferably have no more than a total of 24, in particular no more than a total of 18 and particularly preferably not more than 12 carbon atoms. The Accumulation on the surface of the primary particles formed can, for example via a covalent or ionic bond and / or polar (dipole-dipole change interaction) or van der Waals forces. Preferably, the surface-modifying components one or more functional groups on. The functional groups that carry these compounds are directed first Line according to the surface groups of the resulting ITO powder and beyond even after the desired interaction. Examples of preferred functional Groups are carboxylic acid groups, acid amide groups (primary, secondary and tertiary) amino groups, hydroxyl groups and C-H-acidic groups, as in β-dicarbonyl compounds. Several of these groups can be used simultaneously in one Molecule (betaines, amino acids, EDTA, etc.).

Accordingly, there are examples of the surface modifying components saturated or unsaturated mono- and polycarboxylic acids (preferably Monocarboxylic acids) having 1 to 24 carbon atoms.  

Examples of further suitable surface-modifying components are mono- and polyamines, in particular those of the general formula R _{3 -n} NH _n , in which n = 0, 1 or 2 and the radicals R independently of one another are alkyl groups with 1 to 12, in particular 1 to 6 and especially preferably represent 1 to 4 carbon atoms (e.g. methyl, ethyl, n- and i-propyl and butyl) and polyethylene amines; β-dicarbonyl compounds with 4 to 12, in particular 5 to 8, carbon atoms; Organoalkoxysilanes, such as. B. those used for the surface modification of colloidal silica (z. B. those of the general formula R _4-m Si (OR ') _m in which the groups R and R' independently of one another represent C ₁ -C ₄ alkyl and m is 1, 2, 3 or 4); and modified alcoholates in which some of the OR groups (R as defined above) are substituted by inert organic groups and a bond (condensation) takes place on the particle surface via the OR groups still present and the organic groups take over the shielding. Examples of this are e.g. B. zirconium and titanium alcoholates M (OR) ₄ (M = Ti, Zr), in which a part of the OR groups by a complexing agent, such as. B. a β-dicarbonyl compound or a (mono) carboxylic acid is replaced.

Another group of usable surface-modifying components are Surfactants, e.g. B. cationic, anionic, non-ionic and amphoteric surfactants. Prefers are non-ionic surfactants, with polyethylene oxide derivatives being particularly preferred are. It can be z. B. derivatives with saturated or unsaturated Act (mono) carboxylic acids, especially with carboxylic acids with more than 7, preferably more than 11 carbon atoms, e.g. B. polyethylene oxide derivatives with stearin, Palmitic or oleic acid, such as the products available under the "Emulsogen" brand. It can also be derivatives with sorbitan esters (sorbitan + carboxylic acid), the carboxylic acid being, for example, those mentioned above. These products are commercially available under the "Tween" brand. Can continue Polyethylene oxide (mono) alkyl ether, for example with alcohols with more than 7, is preferred more than 11 carbon atoms are used, e.g. B. the under the brand "Brij" available products.  

Specific examples of usable surface-modifying components are

• a. Mono- and polycarboxylic acids such as formic acid, acetic acid, propionic acid, Butyric acid, pentanoic acid, hexanoic acid, acrylic acid, methacrylic acid, Crotonic acid, citric acid, adipic acid, succinic acid, glutaric acid, Oxalic acid, maleic acid, fumaric acid, itaconic acid, stearic acid and in particular 3,6,9-trioxadecanoic acid and the corresponding anhydrides,
• b. Diketones such as acetylacetone, 2,4-hexanedione, 3,5-heptanedione, acetoacetic acid, acetoacetic acid-C ₁ -C ₄ -alkyl esters such as ethyl acetoacetate, diacetyl and acetonylacetone,
• c. Amino acids, especially β-alanine, but also glycine, valine, Aminocaproic acid, leucine and isoleucine,
• d. Polyethylene oxide derivatives, especially Tween® 80 (sorbitan monooleate polyoxyalkylene), but also Emulsogen® (hexaglycol monostearate), Emulsogen® OG (oleic acid derivative) and Brij® 30 (polyoxyethylene lauryl ether),
• e. Acid amides, especially caprolactam, and
• f. Amines such as B. methylamine, dimethylamine. Trimethylamine, aniline, N-methylaniline, Diphenylamine, triphenylamine, toluidine, ethylenediamine, diethylene triamine.

These surface-modifying components can be used individually or as a mixture be used. Particularly preferred compounds are 3,6,9-trioxadecane acid, β-alanine, Tween® 80 and caprolactam.

The proportion of the surface-modifying component (s), based on the ITO powder, is preferably between 2 and 30 wt .-%, particularly preferred between 2 and 6% by weight.

The precipitation takes place in the presence of the surface-modifying component (s) preferably at a temperature from room temperature (20 ° C) to Boiling point of the solvent. Temperatures in the Range from 20 to 100 ° C. The surface modifying components are usually partially or completely on the surface of the resulting Indium-tin-oxide powder articles deposited. Without being tied to a theory  , it is assumed that the surface-modifying components after removal of the solvent and the calcination at least partially on the Surface of the powder particles can remain. But it is also possible that the Surface-modifying components no longer exist in the end product are.

The solvent is then filtered, for example, by evaporation and / or centrifuging and optionally drying, for example under vacuum and / or elevated temperature (e.g. at temperatures up to 250 ° C or up to 200 ° C) or freeze-dried. The powder obtained in this way these are usually particles from an indium tin oxide / hydroxide mixture, wherein the particles are modified on the surface if necessary.

The powder obtained is then calcined. This is preferred in an oven executed. The calcination takes place, for example, at temperatures between 200 and 400 ° C, preferably between 230 and 280 ° C, particularly preferably 250 ° C. The Isothermal holding time is, for example, between 15 and 120 minutes, preferably between 45 and 90 min, particularly preferably 60 min.

The calcination is preferably carried out under reducing conditions, wherein also apply the process conditions mentioned above come. The reducing conditions are preferred by passage a reducing gas / gas mixture or a reducing steam receive. Before using the reducing component, the furnace can be Inert gas, e.g. B. nitrogen purge. As a reducing gas / gas mixture or reducing steam can, for example, carbon monoxide, Carbon monoxide / nitrogen, a water vapor atmosphere or forming gas (Hydrogen / nitrogen) can be used. The use of Forming gas is particularly preferred. The gas flow used depends on the amount of the powder to be calcined and the reducing component.  

If the powder has not been calcined under reducing conditions, the Reduction can also be carried out after the calcination, for example by Sintering of the powder or molded body under reducing conditions. For Reduction can then also the gases / gas mixtures mentioned above or vapors are used.

The calcined, possibly reduced powder is in this form despite the Use of surface-modifying components through simple Dispersion only incomplete in a suspension with primary particle size, which is usually in the lower nm range.

According to the calcined powder is a crushing or Dispersion treatment with the addition of further surface-modifying agents Components and one or more solvents subjected. The Crushing or dispersing treatment can be done in any conceivable way respectively; it is preferably a comminution treatment. Especially the mechanical comminution treatment and / or the Shredding treatment using ultrasound.

The mechanical crushing step can e.g. B. in mills, kneaders or Roller mills are carried out. Suitable devices for mechanical Comminution are, for example, planetary ball mills, agitator ball mills and especially mortar mills and three-roller mills. The crushing, the z. B. from Grinding and homogenization can be preferred at room temperature executed. The duration depends on the type of mixture and the one used Shredding device.

The comminution or dispersion is carried out with the addition of one or more surface modifying components. In principle, it is about the same compounds that have been mentioned above as surface-modifying Components for use in precipitation have been described. You can in this stage the same compounds as surface modifying components  be used, which were used in the precipitation. Alternatively, you can Different surfaces also during precipitation and crushing modifying components are used.

Organic carboxylic acids and their derivatives, such as anhydrides and acid amides, are preferred as a surface-modifying component in comminution or dispersion used. It will refer to the examples listed above referred. The use of 3,6,9-trioxadecanoic acid is particularly preferred.

When crushing or dispersing, the surface-modifying Component, based on the indium tin oxide powder used, preferably in an amount of 2 to 30% by weight, particularly preferably 2 to 10% by weight, admitted.

The crushing or dispersion is carried out with the addition of one or more Solvents. The solvents can be used as solvents described above for the precipitation step. Prefers but high-boiling liquids are used as solvents. Under high-boiling liquids are z. B. Liquids with a boiling point understood above 120 ° C, preferably above 150 ° C. High-boiling are preferred Glycols or glycol ethers used, for example ethylene, propylene or Butylene glycol or the corresponding di-, tri-, tetra-, penta- or hexamers, and the corresponding mono- or diether, one or both Hydroxy groups by z. B. a methoxy, ethoxy, propoxy or butoxy group are replaced. Other examples are terpenes, e.g. B. terpineol; Polyols, e.g. B. 2-Me ethyl 2,4-pentanediol; and polyethylene glycols and their ethers, such as diethylene glycol, Triethylene glycol, tetraethylene glycol, diethylene glycol diethyl ether, tetraethylene glycol dimethyl ether or diethylene glycol monobutyl ether. Ethylene glycol, diethylene glycol and diethylene glycol monobutyl ether are preferably used. Of course mixtures of two or more of these solvents can also be used , for example in a volume ratio of 2: 1 to 1: 2.  

The solvent can be reduced in size or dispersion, based on the indium tin oxide powder used, in an amount of 5 to 150% by weight, preferably from 10 to 100% by weight, particularly preferably from 30 to 50% by weight be added. A particularly preferred ratio of powder to The solvent is 75:25. The amount of solvent is preferably chosen so that that pasty or highly viscous suspensions are obtained.

The ITO suspension thus obtained can be used directly, for example for coating used for purposes. If necessary, you can increase the Viscosity of other solvents (either the one already used or a other of the solvents described above) are added.

The ITO suspension can also be removed by removing the liquid Components (e.g. by filtering, evaporating, centrifuging and / or drying) an ITO powder can be obtained.

The ITO powder and ITO suspension thus obtained contain more surprisingly wise nanoscale particles, which mainly consist of primary particles and practically not available as aggregates. By the method according to the invention it is therefore possible to powder, suspensions and moldings based on indi To provide tin oxide in which the particle size does not exceed 200 nm is. In particular, particle sizes of less than 50 or less than 20 nm and even from about 10 to 11 nm can be obtained. The particle size is usually over 2 nm, more often above 5 nm. Surprisingly, the so obtained Powder easily z. B. in alcoholic solutions (e.g. ethanol), but also in Water to be dispersed to their full primary particle size, the The above-mentioned particle size is retained, that is, the primary particles without Aggregate formation is retained. Can be used for the dispersion of the ITO powder in principle all suitable solvents are used, for example the solvents described above for the precipitation.  

It is possible to store the indium tin oxide as a powder and if necessary to be used either as a powder, paste or suspension. The preferably used suspension obtained by simple dispersion be and z. B. for coating z. B. by dipping or spraying be used.

From the ITO powder can be known to those skilled in the art Molding process. For example, extrusion, Slip molding, injection molding, electrophoresis, film casting or screen printing called. Depending on the method used, binders can also be used be set. As molded articles, for. B. layers or sintered bodies, in particular targets are produced. Targets are used in particular Sputtering process used to coat substrates. A special The advantage of the materials according to the invention is that for the shaping the molded body is essential compared to the usual indium tin oxide materials lower temperatures are required.

The ITO materials produced according to the invention are preferably found as Coating material in opto and micro electronics or for optical (transparent), IR reflective or conductive coatings use. They can also be used for screen printing pastes. You can are preferably used for transparent control electrodes for Liquid displays, thin film electroluminescent displays, electrochromic dis plays, transparent conductive layers for highly sensitive radiation selectors, ferroelectric photoconductors, memory devices, transparent conductive oxide films as gate electrodes for charge, injection and charge coupled arrangements, as well as for the production of printing pastes, which are suitable for the Printing on glass, ceramics and plastics are suitable for shielding electromagnetic waves, for IR-reflecting layers or plastics, conductive electrodes for solar cells or antistatic films, e.g. B. for television tubes, Monitors and contact screens.  

The following example illustrates the invention without restricting it.

example a) Preparation of the InO (OH) precursor

• - 140 g indium (+ III) chloride (0.63 mol anhydrous)
• - 18 g of tin (+ IV) chloride × 5 H ₂ O
• - 5.6 g caprolactam

are placed in 1400 ml of water and stirred. Having a clear solution is created, it is heated to 50 ° C. After the temperature is reached 105 ml of ammonium hydroxide solution (25%) are added dropwise with vigorous stirring. The Suspension is stirred at a temperature of 50 ° C for a further 24 hours. For complete precipitation, the mixture is then 280 ml Ammonium hydroxide solution added. A white precipitate forms Indium oxide hydroxide, which is centrifuged off (30 min at 4000 rpm). The powder is dried in a vacuum drying cabinet at 190 ° C until a light one Yellowing of the powder is observed (transition to crystalline indium oxide).

b) aftertreatment of the dried indium oxide hydroxide

The dried powder is finely ground, distributed in crystallizing dishes and in a forming gas furnace. The furnace is evacuated, then flooded with nitrogen. The furnace is heated at a heating rate of 250 ° C / hour to 250 ° C at one Nitrogen flow of 200 liters / hour. This temperature is below for 60 minutes Forming gas atmosphere maintained at a gas flow of 300 liters / hour. After that the furnace cools down to room temperature under a nitrogen atmosphere (duration: approx. 5 Hours). This results in a dark blue powder, which by X-ray analysis was identifiable as pure indium oxide phase.  

c) working up of the indium oxide powder

25 g of a mixture of ethylene glycol are placed in a mortar mill, Dibutylene glycol ether (alternatively, diethylene glycol for ethylene glycol and / or Diethylene glycol monobutyl ether can be used for dibutylene glycol ether) as well 5.6 g of 3,6,9-trioxadecanoic acid. 75 g of ITO powder are slowly added and it is ground for 1 hour. Then there is a dark blue highly viscous Suspension which is homogenized in a roller mill for approx. 20 minutes. The so suspension obtained is redispersed in ethanol and for coating purposes used.

Separation of the ethanol gives ITO powders which can be redispersed in ethanol to a particle size below 20 nm. The primary particle size is 10 to 11 nm, the specific surface area is 70 m ² / g. Isoelectric point: 7.2. The tin content is usually 8 mol%. These powders can be used to apply sol-gel layers that can achieve a transmission <90% and a sheet resistance of 160 Ω / at a film thickness of 400 nm at a baking temperature of 550 ° C on glass. It is possible to apply several layers, whereby the surface resistance is further reduced. The surface resistance achieved with a two-layer (600 nm layer thickness) is already 100 Ω /.

Claims (11)

1. A process for the preparation of suspensions, powders and moldings of indium tin oxide, characterized in that

• a) indium oxide and tin oxide precursors are precipitated from solutions in one or more solvents in the presence of one or more surface-modifying components,
• b) the powder obtained is calcined after removal of the solvent,
• c) one or more surface-modifying components and one or more solvents are added,
• d) the mixture obtained is subjected to a grinding or dispersing treatment,
• e) if necessary, liquid components are separated off in order to obtain a powder,
• f) optionally the powder obtained is converted into a shaped body by means of a shaping process.

2. The method according to claim 1, characterized in that as indium and Tin oxide precursors indium (+ III) chloride, indium (+ III) iodide, indium (+ I) chloride, Indium (+ I) iodide, indium (+ III) nitrate, indium (+ III) acetate, indium (+ III) sulfate and / or indium (+ III) alkoxides or tin chloride, tin sulfate and / or Tin alkoxides are used, with tin in the oxidation state +2 or +4 is present. 3. The method according to claim 1 or 2, characterized in that as surface-modifying component in the precipitation and / or in the Comminution or dispersion of mono- or polycarboxylic acids, diketones, Amino acids, polyethylene oxide derivatives, amines or acid amides or Mixtures of two or more of these components are used.   4. The method according to claim 3, characterized in that 3,6,9-trioxadecanoic acid, β-alanine, Tween® 80 and / or caprolactam as surface-modifying components are used. 5. The method according to any one of claims 1 to 4, characterized in that a base is used to precipitate the indium oxide and tin oxide precursors. 6. The method according to any one of claims 1 to 5, characterized in that the calcination is carried out at 200 to 400 ° C. 7. The method according to any one of claims 1 to 6, characterized in that is calcined under reducing conditions or that after the Calcination is reduced. 8. The method according to any one of claims 1 to 7, characterized in that comminution in a high-boiling solvent, in particular Diethylene glycol or diethylene glycol monobutyl ether is carried out. 9. suspensions, powders and moldings based on indium tin oxide, obtainable by the process according to any one of claims 1 to 8. 10. Use of the indium tin oxide materials according to claim 9 as Coating material for micro and optoelectronic purposes. 11. Use of the indium tin oxide materials according to claim 9 for transparent, IR-reflective or conductive coatings or for Screen printing pastes.